Abstract
A positive deviation from the Matthiessen's Rule (DMR) of solute Zn in Mg was previously predicted. To confirm and to quantitate the above prediction, Mg–Zn alloys containing up to 10%Zn were prepared and, after long period solution treatment, dependences of resistivity on Zn concentration and on temperature of resistivity measurement were investigated. The completion in dissolution of eutectic precipitates was confirmed by optical micrography, X-ray diffractometry and saturation of decrease in resistance ratio by isothermal solution treatment. Resistivity of perfect solid solutions up to 6.70 mass (2.60 at)%Zn shows a good linear relationship to f(X) =X(1−6.16X), where X is atomic fraction of solute Zn obtained by chemical analysis of the resistivity specimen, as
43.8<ρD300/nΩm=[1075.8X(1−6.16X)+43.8]±0.4<67.0
5.2<ρD77/nΩm=[992.4X(1−6.16X)+5.22]±0.1<26.6.
These relations, which should be called as corrected Nordheim's Rule, give contribution per unit concentration of solute Zn to resistivity, ΔρZn/nΩm (at%)−1, as 10.76 at 300 K and as 9.92 at 77 K. dρ/dTmeasured between 280 and 305 K increases with X, also corresponding to the positive DMR of solute Zn in Mg. Ratio of these ΔρZn at 300 K and 77 K, η=Δρ300/Δρ77, is 1.088. However, next relation employing η= 1.093 gives the smallest intercept of regression line and is recommended as DMR corrected empirical relation,
5.2<ρD77/nΩm=[37.98/(R−1.093)]±0.1<26.6.
